The aims of the European Organization for Research on Treatment of Cancer (EORTC) are conducting, developing, coordinating and stimulating research in Europe on the experimental and clinical bases of treatment of cancer and related problems. Extensive and comprehensive research in this wide field is often beyond the means of the individual European laboratories and hospitals and can be best accomplished through the joint efforts of the clinical and basic research groups of several countries. EORTC has initiated five major efforts in the field of cancer treatment: (1) a screening program of potential anticancer agents, (2) the organization of clinical and preclinical cooperative groups aimed at carrying out controlled clinical trials (multicenter phase I,II,III) with new therapeutic agents and regimens, (3) the organization of collaborative research programs, (4) a fellowship program to enable clinicians and research workers to study and work in EORTC institutions outside their own country, (5) the initiation of symposia, courses and publications on the subject of cancer research and treatment. To assist the groups in their scientific work, the EORTC Coordinating Office was established in 1969 and expanded in an EORTC Coordinating and Data Center in 1974. The purpose of the Coordinating and Data Center is to provide central coordination for the activities of the EORTC groups and to make available to the groups a wide range of statistical and data processing expertise, including advice on study designs as well as analysis and reporting of results, at a central, and hence economical location. The Data Center, which is situated at the Institut Jules Bordet in Brussels, uses two powerful CDC computers located at the Brussels FREE University. Its full time staff comprises 2 MD, 3 statisticians, 3 computer analysts, 7 data managers and 4 secretaries. At present, the Data Center monitors 70 clinical studies involving approximately 7000 patients from 165 institutions and clinical services in 21 countries.